Vertical shaft impact crushers (VSI-crushers) are used in many applications for crushing hard material like rocks, ore etc. A VSI-crusher comprising a housing and a horizontal rotor located inside the housing is described in WO 2004/020103. A first flow of material to be crushed is fed to the rotor via an opening in the top thereof, is accelerated by the rotor, and is ejected towards the wall of the housing. An optional second flow of material may be fed outside of the rotor, i.e., between the rotor and the housing. This second flow of material is impacted by the first flow of material ejected by the rotor.
In some situations the operation of the crusher described in WO 2004/020103 may be disturbed by problems in the feeding of the first flow of material to the rotor, resulting in a reduced crushing efficiency of the VSI-crusher.